Dielectric material



5o' o 1o so 9o' loo rups/:Amps l/v oec/rees senr/amos so 4o' FIG. 4

so eo 4o zo TEMPERATURE /N @senses cm1/amos 'IIIIIIIIIIII Awanm 0 Aug.9, 1938.

Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE Yager, Livingston,

N. d., assignors to Bell Telephone Laboratories, Incorporated, New York,N. Y., a corporation of New York Application March 28, 1935, Serial No.13,438

(Cl. S-12) 26 Claims.

This invention relates to dielectric materials for use in electricaldevices, and more particularly to such materials for use in capacitors,Wave guides and the like which are adapted to 5 the use of either aliquid or a solid material, either alone or in combination with a porousnon-conducting material such as paper.

An object of this invention is to provide dielectric materials of highdielectric constant for use in electrical apparatus such as capacitors,Where it is desired to secure a maximum of cam pacity consistent withother desirable electrical and physical characteristics.

Another object oi this invention is to secure dielectric materialswhich, under the conditions of use, will be solids and which will,either alone or in conjunction with another dielectric such as paper,provide high capacity in electrical apparatus, and which at the sametime Will have the physical properties, such as melting points,

compressibility, viscosity, and penetrative properties, which make themreadily applicable to such apparatus.

Another object of this invention is to secure dielectric materials whichare soluble in common organic liquids, so as to be suitable for use insolutions, mixtures or pastes, and which are also compatible with otherorganic solids, so as to permit their use in mixtures having more de 30sirable melting points, fluidities, and penetrabilities than thematerials themselves.

Another object of this invention is to provide dielectric materialshaving a high dielectric constant which is retained at high frequencies.

Another object of this invention is to provide dielectric materials of aWater-proof or nonhydroscopic character, and which do not undergoelectrolytic changes under the conditions of use in electricalapparatus.

Another object of this invention is to provide a dielectric materialwhich changes its dielectric constant sharply at a certain temperatureor Within a certain range of temperatures, without undergoingliquefaction.

Another object of this invention is to provide a dielectric material,which when used in conjunction With paper Will yield a capacitor havinga low temperature coeicient of capacitance.

To accomplish these objects and in accordance with one feature o f theinvention, a group of dielectric materials is provided which may bedefined as polar derivatives of polymethylene cyclic carbon compounds,the dielectric constants of which in the crystalline state are as highor higher than in the liquid state.

In accordance with another feature oi the invention one or more of thesematerials is combined with an organic material such as an insulating Waxor a hydrocarbon oil to alter the physical properties oi'the dielectricWithout materially ali'ecting its electrical properties.

In accordance with still another feature of the invention thesematerials may be used either alone or in combination With paper or otherporous material as the non-conducting sheets of a capacitor.

It is 'Well known that many materials have a high dielectric constant inthe molten or liquid state, but that on passing into the crystallinesolid form at the melting point, the dielectric constant of thesematerials decreases to a low value of about 3. 'Many other materialshave lO-W values of dielectric constant in the liquid state whichincrease slightly, in proportion to the increase in density onsolidiiying, but still have low values of the dielectric constant, thatis, about 3. The dielectric constant of these classes of materials inthe solid state is approxi:- mately equal to the square of theirrefractive index. We have discovered that the following materials, dcamphor (natural gum camphor), d-l-camphor (synthetic camphor),camphoric anhydride, borneol, isoborneol, bo-rnyl chloride (pinenehydrochloride), cyclohexanol, chlorocyclohexane and cyclohexene to whichthis invention relates, have dielectric constants in the crystallinesolid state as high as, or higher than, in the liquid state, and alsohigher than the square of the refractive index for visible light for therespective materials. Also, these materials are applicable asdielectrics in electrical apparatus, where they possess the desirablephysical characteristics of solids and yet retain the high dielectricconstants usually found only in liquids. There are two kinds of solids,that is, crystalline solids which show a regular arrangement of atomicor molecular building units in an X-ray photograph and glasses oramorphous materials which show a random arrangement of atomic ormolecular units. Just as the dielectric behavior of the materials ofthis invention difiers from that oi others which solidify to crystallinesolids, their behavior also differs from those materials which solidifyto glasses, or amorphous, or non-crystalline.solids, in a Way which willbe described later.

We have also discovered that the foregoing substances to Which thisinvention relates have the characteristic that with increasingtemperature, the solid crystalline substances undergo at sometemperature below the melting point, sheets of which are made oi paperimpregnated transition from a solid crystalline state ci low withcyclohexanol;

dielectric constant to a solid crystalline state Fig. 5 shows anembodiment oi the invention of high dielectric constant, withoutundergoing in which applicants material is employed as an 5liquefaction. With decreasing temperature, the impregnating material forthe porous non-con- 5 transition is from a state of high to a state ofducting sheets of the capacitor; low dielectric constant. it thistransition point, Fig. 6 shows in cross-section a modified capaciadiscontinuous change of density has been obtor structure in which thedielectric material served in the materials to which this invention ofthis invention is applied directly tc the conm relates, the change beingfrom a higher density ducting sheets of the capacitor and used incombelow the transition point to a lower density bination with sheets ofinsulating material; and above the transition point or vice versa; thisFig. '7 shows in cross--section a structure simchange being observed onapproaching the 'tranilar to that of Fig. 6 in which the insulatingSition temperature from either direction. [in sheets are eliminated.

evolution of heat on passing through the transi- Referring to thedrawing, Fig. l, shows a tenn 15 tion point in the direction. ofdecreasing *tern* perature hysteresis curve of the transition forperature has also been observed in these roated camphor. For decreasingtemperatures, shown rials, and a corresponding absorption of heat on oncurve A, the transition taires place at 37 C. passing through thetransition with increasingr while for increasing temperatures, as shownon temperature. It has also been iound that the curve B, transitiontakes place at 30 C. Sim 20 specific heat follows the saine generalbehavior ilar hysteresis curves are shown on Fig. 2 in as the dielectricconstant, having a higher value which curve A shows the hysteresis inthe transiabove the transition point than below it. tion for isoborneolwith a descending tempera A practically important feature of these mateture and curve B shows the similar transition rials is their highdielectric constant in the for ascending temperatures. With thismaterial 25 solid state at temperatures above a transition it will benoted that the hysteresis is spread out point. Some of the propertiesserve only to deover a much wider range of temperatures than scribe andidentify the materials as belonging was the case for d caniphor shown inFig. l. to the class to which this invention relates. Curve C of Fig. 2is a corresponding curve for In the following table are shown thetransition borneol in which it will be noted that there is 30temperatures, dielectric constants and densities no hysteresis of thetransition, the values oi above and below the transition temperature ofdielectric constant for ascending descending certain of the materials towhich this invention temperatures falling on the same curve in thisrelates: case. For the materials illustrated by Figs. i

Approximate Dielectric Dielectric Density Density Compound transition.tn mconstant constant below above pointure (rising above below tiansitransiternp.) transition transition tion tion l0 domnphor 30 12.52.7 Loss 1.003 i d-l Camphor wG5 11.5 2. 9 1.066 1.026 Cnmphoricanhydride +l 21.5 2. 5 Borncol," 72 3. 9 2. il Isoborncol. +25 ll. l 2.i) lornyl chlor 115 7.0 2.5

CyclohcxanoL.- 28 20.3 2.5 5 Chlorocyclolicxa o-. -o 10.8 2,9

Substances capable of undergoing such a and 2, the dielectric constantcurves shown are transition with respect to dielectric properties thesame for all frequencies from Gil to lil 5U will be referred tohereafter as transition dieleccycles per second. In some of thetransition dl- ,3U trios and the temperature at which such transielectrics a dependence or" the dielectric constant tions occur will bereferred to as transition temupon frequency has been observed. Forexample, peratures. The transition from one solid form with d-l camphor,the change in capacity in- '00 the Oher Which these matel'llS ShOW, dOeSdependent oi frequency for temperatures above 55 not in all cases takeplace sharply at one tem Q(l" C. but below that point it has adielectric 5:) perature, but may 000111' over a range of tem constantwhen measured at ico ki1ocyo1os,some peratures. Also, the temperature atwhich the what below that when employing a hey transition takes placewith decreasing temperal kilocycle. Bornyl chloride be.' .aves 'larhzture may be different from that with increasing The dielectric constantabove the trans. io l. -id

uo temperature. This behavior is hereafter referred during a part of itscourse through the transition mi to as a hysteresis of the transition.is independent or frequency. but lower een The invention both as to itsfurther objects peratures depends somewhat upon frequency. in andfeatures will be more clearly understood from these cases the frequencybehavior is the same, the following detailed description taken togetherirrespective of whether the transition apwith the accompanying drawingin which: proached with ascending or descending teinpcra- 455 Fig. 1shows the dielectric constant and temtures. perature hysteresis oftransition of d camphor; A still diierent type of dielectric behavior inFig. 2 similarly shows the dielectric constant the transitiondielectrics is illustrated by Fig. 3 and temperature hysteresis ofisoborneol and for cyclohexanol. Starting at low temperatures borneol;with the dielectric in the low temperaiure crys- To Fie. 3 Shows thedielectric constant and temtalline form, the dielectric constant isindependperature hysteresis of cyclohexancl at dierent ent of frequencyand increases sharply at the frequencies; transition point to its highvalue along curve B,

Fig. 4 shows the change in capacity at various still essentiallyindependent oi frequency. Starttemperatures fora capacitor, thenon-conducting ing from higher temperatures, however, the 75 transitiondoes not take place at the same temperature but shows a hysteresis andone which is dependent upon frequency in the manner shown. Curve A for100 kilocyoles begins to decrease at a higher temperature than curve A'for 10 kilocycles. Curve A for 1 kilocycle decreases at still lowertemperatures. At the temperature indicated by the dotted line thesupercooled material recrystallized to the low temperature form. Thepurity of the material has been found to be one factor, though notnecessarily the only one, which may cause this observed supercooling anddependence of dielectric constant upon frequency. Knowledge of the factand temperature of transition, and of the hysteresis which may bepresent, permits one to bring about solidication under conditions so asto insure the presence of either form as desired.

Examination of the accepted chemical formulae for the transitiondielectrics shows them to be polar derivatives of polymethylene cyclichydrocarbons. Ihey may be mono-cyclic as in cyclohexanol or polycyclicas in borneol. They may consist of rings of five like atoms as in thepolycyclic terpene derivatives or of six like atoms as in cyclohexanol.The substances exhibiting the dielectric transition phenomena contain atleast one substituent group of polar type so situated as to lead to itsclassification as a polar compound. This polar group may be carbonyl asin camphor, hydroxyl as in borneol, isoborneol or cyclohexanol, orchlorine as in bornyl chloride or chlorocyclohexane. Or they may containtwo polar groups as in the anhydride structure of camphoric anhydride.Or the polar group may be an oxime as in camphor oxime. Or polarity maybe contributed by partial unsaturation as in cyclohexene.

While the previous examples describe polar derivatives of polymethylenehydrocarbons which contain only carboxyl, hydroxyl, chlorine or oximegroups or which have an anhydride structure or which are partiallyunsaturated other derivatives may be used as well. For example, themethyl, ethyl or other alkyl substituted derivatives or ,the nitro, ornitrile, or methoxy, or carboxy, or ester derivatives of polymethylenecyclic hydrocarbons may be used. We do not eX- clude other substitutedgroups, such as bromine or iodine, but prefer the substituted groups oratoms of lower atomic weight.

'I'he magnitude of the dielectric constant which these transitiondielectrics have in the solid state is related to the polarity of thesubstituent group and the arrangement of these polar groups in thecyclic structure. For the highest values of dielectric constant, thepreferred substituent groups are nitro (NO2), nitrile (CN), carboxyl(CO), chlorine (Cl) and hydroxyl (OH). The preferred arrangement ofthese groups in the case of compounds containing more than onesubstituent group is an asymmetrical one. For example, ortho-dichlorocyclohexane is preferred to paradichloroxyclohexane.

The temperature at which the transition occurs is related to theintermolecular forces acting in the solid and to the chemical nature ofthe substituent group, although in a complicated manner. For a lowtransition temperature, the preferred case is a solid of lowintermolecular forces or internal elds.

The transition dielectrics to which this invention relates are,therefore, described and distinguished by the fact that they are polarderivatives of polymethylene cyclic carbon compounds.

The following substances which resemble one or more of the substances towhich this invention relates in some feature of chemical constitution donot exhibit the above described transition. Hexane is a saturatedhydrocarbon but is not a transition dielectric, being non-polar andnon-cyclic. Chlorobenzene is a cyclic, polar substituted hydrocarbon,but is not a transition dielectric, being an aromatic, or aryl cyclicrather than polymethylene compound. Benzoic anhydride is a cyclic polarsubstituted compound having an anhydride structure, but it is not atransition dielectric, being an aromatic cyclic compound. In this way wedistinguish transition dielectrics from all other classes of dielectricsin that they are polar derivatives of polymethylene cyclic hydrocarbons.

In Fig. 5 the invention is shown as embodied in a capacitor unit of therolled type, which consists of a pair of conducting sheets I0, Ialternating with sheets Il, Ii of porous non-conducting material such aspaper or textile fabric, these sheets being impregnated with adielectric material containing a polar derivative of polymethylenecyclic carbon compounds. The nonconducting sheets II, II may beimpregnated before their assembly in alternate position with theconducting plates and then wound, but preferably the non-conducting andconducting sheets are wound into a unit and then impregnated withinsulating material.y Terminal members I2, I2 are provided as shown topermit connecting the respective conducting sheets in an electricalcircuit.

In the modied construction as shown in crosssection in Fig. 6 thedielectric material of this invention is applied directly as coatingsI4, I4 to the conducting sheets I', Iii. Insulating sheets I5, I5 arepositioned as shown and the assembled sheets wound into unit form asshown on Fig. 5. The structure of Fig. 7 differs from that of Fig. 6only in that the insulating sheets I5, i5 are dispensed with. Thedielectric materials of this invention are also applicable to the use inthe stacked type of capacitor in which the conducting plates instead ofbeing rolled are formed into a stack in the well-known manner.

The paper insulated capacitor of the type shown in Fig. 5 and designedfor operation at low voltage, 500 volts or less, having cubicaldimensions of 13.3 om3 has, when impregnated according to standardpractice with chlorinated naphthalene, a commercial dielectric, acapacity of 1.0 microfarad. When such a paper insulated capacity unit issimilarly impregnated with cyclohexanol, its capacity is increased toapproximately 1.4 microfarads, an increase of approximately 10%. If noincrease of dielectric capacity is desired, the size of the capacitormay be reduced when impregnated with the materials to which thisinvention relates. For example, a on-e-microfarad capacitor of the typeillustrated in Fig. 5 when impregnated with chlorinated naphthalene orchlorinated diphenyl has a cubical volume of 13.3 cm3. When impregnatedwith cyclohexanol the one-microfarad capacitor of correspondingdielectric thickness need have a cubic volume of only 9.5 cm3.

Due to the fact that the temperature coeflicient of dielectric constantof Ycyclohexanol has the opposite sign from that of paper over aconsiderab-le range of temperatures, a paper insulated capacitor of thetype disclosed in Fig. 5

scopic and non-water soluble.

zero or a` very small temperature coenioient of capacitance over a widetemperature range. This is clearly illustrated in Fig. 4 of attacheddrawing which shows that over the temperature range from 20 C. to +40 C.the capacity measured at a frequency of 30,000 cycles changes only to avery slight degree. A paper insulated condenser impregnated withcyclohexanol was found to change its capacity at the transition point byapproximately 100%. In other cases using these transition dielectricsfor impregnating paper condensers similar changes of 25% or more takeplace. Dielectric constants of the solids previously listed in tabularform range from 4 to 24 as shown and the transition points range from115 C. to +135 C. Therefore, capacitors may be prepared fromcombinations of these or other transition dielectrics with paper, forexample, having a wide range of capacities and a great variety oftemperature characteristics.

Heretofore, it has been common practice to use as separator incapacitors intended for impregnation a relatively dense paper, becausethe dielectric constant of the cellulosic material constituting thepaper is higher than that of the available dielectric materials suitablefor impregnation. With these new dielectric materials the dielectricconstant of the paper is no longer the limiting factor but highercapacities can now be obtained by the use of more porous paper and hencea larger percentage of impregnating material.

The use of dielectric materials undergoing such a transition is notlimited to the pure forms of the materials. In suspensions, mixtures orpastes, where there is some transition dielectric present as a solidphase, the transition is observed.

Some of the transition dielectrics described herein melt at temperaturestoo high to permit their use alone for impregnating condensers accordingto the usual procedure. Such transition dlelectrics may, however, beused in solutions or mixtures with other dielectric materials such asmineral oil, rosin oil, chlorinated diphenyl, halowax or superlawax, insuch a manner as to retain the advantage due to their high dielectricconstant. In such mixtures the dielectric constants represent roughly amean between the dielectric constants of the two componentsapproximately in proportion to the molar fraction of each.

A paper insulated capacitor of the type disclosed in Fig. 5, whenimpregnated with a solution of chlorinated diphenyl containing 40% byweight of d camphor, had a capacity approximately 25% higher than asimilar capacitor similarly impregnated with the chlorinated diphenylalone. 'I'his 40% solution of d camphor in chlorinated diphenyl was notsaturated with respect to camphor at room temperature. At C., a moresuitable temperature for impregnation, the d camphor is soluble to theextent of 60% and good impregnation results. A 60% solution of d camphorin chlorinated diphenyl is supersaturated with respect to d camphor atroom temperature and a mush or paste results on cooling. Capacitorsimpregnated with the 60% solution had about 30% higher capacity thanthose impregnated with chlorinated diphenyl alone. This mixture isessentially non-hydro- It does not unwhen impregnated with cyclohexanolmay have dergo electrolytic changes under conditions of measurement.

These transition dielectrics when intimately mixed with certain organicmaterials, by melting the two to a homogeneous solution and thensolidifying, may show either of two types of dielectric behavior. In oneof these, to be designated as solid mixtures of type A, the transitionpoint of the mixture is the same as that of the pure transition materialand the value of the dielectric constant is roughly proportional to themol fraction and dielectric constant of the transition dielectric.Mixtures of d camphor with phthalic anhydride (having 9, 21 and 37 mol.

per cent phthalic anhydride) are examples of this type. In the other ofthese, to be designated as solid mixtures of type B, the transitionpoint is displaced by the presence of the second solid. Mixtures oi' dcamphor with camphoric anhydride containing 25, 50 and 75 mol. per centof d camphor show a progressive lowering of the transition point ofcamphoric anhydride. In this way, mixtures may be prepared having thetransition point at any temperatures desired. For satisfactory operationit is desirable that these mixtures be liquid above C. and solidify atapproximately 50 C.

'Io obtain mixtures of transition solids with other solids having thedielectric behavior of type- A solid mixtures, the preferred choice ofthe second component is one which forms simple eutectic mixtures withthe transition solid.

We have made a theoretical study of the matter in order to establish asound basis for defining the class of materials to which this inventionrelates. According to our study oi the matter, the theoreticalinterpretation of the phenomenon of transition is as follows. Thedielectric constant of a material may be expressed in terms of itsdielectric polarizability or the ability of the electric charges to bedisplaced by an electric field. There are many equations for thisrelationship but the preferred one is tric constant. lIhepola-rizability may be mathematically dened by the equation 'I'nepurpose of this equation is to show that p, the polarizability, andhence K, the dielectric constant, may be dened in terms of fj, aconstant depending upon the restoring force which opposes thedisplacement of any charge, for example, oi the ith type, mi, a constantdepending upon the mass of the charged particle, of the ith type, forexample, and rj, a constant depending upon the frictional resistance tothe displacement of the charged particle, of the ith type, for example.

These are also the factors which determine the vibrations or rotationsof charges or groups of charges of which the material is composed. Themotions of the charges within a dielectric may, for the purpose ofillustration, be regarded as separable into vibrations or rotations ofthe electrons or atoms, or groups of atoms, or molecules or groups ofmolecules, which may be regarded as the units oi which the dielectric iscomposed. Each of these vibrations or rotations has a characteristicfrequency and amplitude and it is the summation of the effect of anelectric field upon these vibrations and rotations which determines thedielectric behavior of any material.

The dielectric constant of a material is affected by all of the factorswhich affect the vibrations or rotations of the atoms or molecules, orgroups of atoms or molecules. These factors include temperature,pressure, voltage, frequency and factors, such as internal field, whichdetermine the state of aggregation of the material. On this basis,reasonable explanations of the effects of these factors upon dielectricbehavior have been developed and described in the literature.

The high dielectric constant of certain substances in the liquid stateis due largely to the fact that their molecules or aggregates ofmolecules which act as the unit possess permanent electric dipoles andare, therefore, classed as polar dielectric materials. A molecule issaid to possess a permanent electric dipole when it is electricallyasymmetrical, that is, when the center of gravity of the positivecharges is separated from the center of gravity of the negative chargesby a nite distance. A molecule containing a permanent electric dipolewill tend to orient itself in an electric field analogously to thewellknown behavior of a permanent magnet orienting itself in a magneticfield.

Among organic materials of the sort to which this invention relates,there is but little difference in dielectric constant, apart from thatdue to the permanent dipole. For example, benzene, hexane, naphthalene,paraffin, cyclohexane, carbon tetrachloride, and other symmetrical ornonpolar materials all have dielectric constants in the liquid statebetween two and three, these being considered low values. Substitutionof polar groups in these materials increases the dielectric constant byan amount which depends upon the polar group. For example, liquidnitroben- Zene has a. dielectric constant of 34 as compared to 2.3 forbenzene. Liquid chlorobenzene has a dielectric constant of 5.5, thechlorine being less polar than the nitro group. These materials aredistinguished from transition dielectrics in that their dielectricconstants decrease to a value between 2 and 3 at their freezing points.The position of substitution determines the dielectric constant. Forexample, ortho-dichlorobenzene has a dielectric constant approximatelyl0, while paradichlorobenzene, which differs in that the substitutedgroups are symmetrically located, has a dielectric constant of only 2.5in the liquid state.

The concept of dielectric behavior which has been outlined is the basisfor expecting that the dielectric materials of this invention, beingpolar, should have high dielectric constants in the liquid state, wherethe polar molecules are free to orient themselves. The only furtherrequirement to account for the high dielectric constants in the solidstate is to show that molecules or parts of molecules are also able toorient or rotate in the solid state, at least in one direction, andwithin certain limits. Recent theoretical and experimental study hasproduced a basis for believing that rotation is possible in the solidstate.

The materials to which this invention rela-tes` belong toa class havinga transition within a range of temperatures at which some rearrangementof the forces holding the molecules together takes place, such that theinter-molecular forces are weakened to an extent that at highertemperatures they are able to take up, from whatever source, enoughenergy to cause them to rotate.

It is an essential part of our invention that we have discovered thatthe preferred class of dielectric materials to provide high dielectricconstants in the solid state is the polymethylene cyclic polarsubstituted hydrocarbons. Although the theory of dielectric behavioroutlined above very completely describes our experimental observations,we do not limit our invention to this theoretical interpretation norconfine ourselves to such substances to which this interpretation mayultimately be found to apply.

What is claimed is:

1. A dielectric material for` electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene cyclic carbon compoundwhich in the solid state undergoes a transition in dielectric propertiesat a particular temperature.

2. A dielectric material for electrical apparatus comprising as a majorconstituent a substance capable of undergoing a transition in the solidstate, at a particular temperature, from a state of high -dielectricconstant to a state of lower dielectric constant.

3. A dielectric material for electrical apparatus comprising a substancecapable of undergoing a transition in the solid state, within a range oftemperatures, passing from a state of high dielectric constant to astate of lower -dielectric constant with decreasing temperature and froma state of low dielectric constant to a state of higher dielectricconstant with increasing temperature.

4. A dielectric material for electrical apparatus comprising as a majo-rconstituent comprising a polar derivative of a polymethylene cyclichydrocarbon having a dielectric constant in the solid state, above atransition, greater than four, which value is substantially independentof frequency between sixty cycles and ten million cycles per second.

5. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene cyclic hydrocarbonhaving a dielectric constant in the solid state above a transitiongreater than the square of the optical refractive index of the materialfor visible light.

6. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene cyclic hydrocarbonhaving a dielectric constant in the solid state, greater than four,which value increases with decreasing temperature in the range oftemperatures between the melting point and the transition point.

7. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene cyclic hydrocarbonwhich is essentially non-hydroscopic and non-water soluble.

8. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene cyclic hydrocarbonwhich is substantially free from electrolytic changes under theconditions of use in electrical apparatus.

9. A dielectric material for electrical apparatus comprising a mixtureof a polar derivative of a polymethylene cyclic hydrocarbon which in thesolid state undergoes a transition in dielectric properties at aparticular temperature with other dielectrics, said mixtures beingmolten above 100 C. and solid below 50 C.

10. A dielectric material for electrical apparatus comprising a mixtureof a polar derivative of a polymethylene cyclic hydrocarbon which in thesolid state undergoes a transition in dielectric properties at aparticular temperature with other dielectrics, said mixture being ahomogeneous solution at 1000 C. and a suspension or paste of crystallinetransition dielectric in a liquid phase composed mainly of the secondcomponent below C.

11, A dielectric material for electrical apparatus comprising a mixtureof a polar derivative of a polymethylene cyclic hydrocarbon Which in thesolid state undergoes a transition in dielectric properties at aparticular temperature with a non-polar dielectric, said polymethylenecyclic hydrocarbon comprising a major portion of said mixture.

12. A dielectric material for electrical apparatus comprising a polarderivative of a polymethylene monocyclic hydrocarbon which in the solidstate undergoes a transition in dielectric properties at a particulartemperature.

13. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene bicyclic hydrocarbonwhich in the solid state undergoes a transition in dielectric propertiesat a particular temperature.

14. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a cyclic terpene which in the solidstate undergoes a transition in dielectric properties at a particulartemperature.

15. A dielectric material for electrical apparatus comprising a polarderivative of a polymethylene monocyclic hydrocarbon having a-dielectric constant in the solid state above a transition greater thanthe square of the optical refractive index of the material for visiblelight.

16. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene bicyclic hydrocarbonhaving a dielectric constant in the solid state above a transitiongreater than the square of the optical refractive index of the materialfor visible light.

17. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a cyclic terpene having a dielectricconstant in the solid state above a transition greater than the squareof the optical refractive index of the material for Visible light.

18. A dielectric material for electrical apparatus comprising a polarderivative of a polymethylene monocyclic hydrocarbon having a dielectricconstant in the solid state greater than four, the value of thedielectric constant increasing with decreasing temperature in the rangeof temperatures between the melting point of said derivative and thetransition point'thereof.

19. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a polymethylene bicyclic hydrocarbonhaving a dielectric constant in the solid state greater than four, thevalue of the dielectric constant increasing with decreasing temperaturein the range of temperatures between the melting point of saidderivative and the transition point thereof.

20. A dielectric material for electrical apparatus comprising as a majorconstituent a polar derivative of a cyclic terpene having a dielectricconstant in the solid state greater than four, the value of thedielectric constant increasing with decreasing temperature in the rangeof temperatures between the melting point of said derivative and thetransition point thereof.

21. A dielectric material for electrical apparatus comprising as a majorconstituent a polar -derivative of a polymethylene cyclic hydrocarbonwhich in the solid state undergoes a transition in dielectric propertiesat a particular temperature, said derivative having one polarsubstituent.

22. A dielectric material for electrical apparatus comprising a polarderivative of a polymethylene cyclic carbon compound Which in the solidstate undergoes a transition in dielectric properties at a particulartemperature, said derivative having two polar substituents.

23. A dielectric material for electrical apparatus comprising as a majorconstituent an asymmetric polar derivative of a polymethylene cyclichydrocarbon which in the solid state undergoes a transition indielectric properties at a particular temperature.

24. A dielectric material for electrical apparatus comprisingiso-borneol.

25. A dielectric material for electrical apparatus comprising camphoricanhydride.

26. A dielectric material for electrical apparatus comprisingcyclohexanol.

ADDISON H. WHITE. WILLIAM A. YAGER.

